Outcasts is set in the middle of the twenty-first century on Carpathia, a "Goldilocks" planet five years' travel from Earth (named after the RMS Carpathia, the ship that went to rescue the Titanic). Carpathia is being colonised by a succession of spaceships arriving from Earth. Most of the planet's population live within the pioneer town of Forthaven, first settled ten years ago. The Carpathians live in ignorance of Earth's fate, receiving news only through the few evacuee transporter ships that successfully achieve the difficult atmospheric entry to Carpathia.

The story focuses on the President, Richard Tate, and core members of the Protection and Security (PAS) team, as well as expeditionaries, whose role is to explore the planet and retrieve resources and medicines. With the arrival of CT-9 – perhaps the last transporter that will reach Carpathia from Earth – storylines involve the ongoing lives of the existing settlers, the induction of new evacuees into the Forthaven community and the effect of others living outside its walls unknown to most of the settlers.